Process for transitioning between incompatible catalysts

ABSTRACT

The invention relates to a process for transitioning from a first continuous polymerization reaction in a gas phase reactor conducted in the presence of a first catalyst to a second polymerization reaction conducted in the presence of a second catalyst in the gas phase reactor wherein the first and second catalysts are incompatible, the process comprising: (a) discontinuing the introduction of the first catalyst from a first catalyst feeding system into a reactor; (b) introducing a catalyst killer to at least partially de-activate the first catalyst in the reactor (c) introducing into the reactor a second catalyst from a second catalyst feeding system separate from the first catalyst feeding system.

This application is a national stage application of PCT/EP2015/080943,filed Dec. 22, 2015, which claims priority to European PatentApplication Number 14199685.0 filed Dec. 22, 2014, both of which arehereby incorporated by reference in their entirety.

This invention relates to a process for transitioning betweenincompatible polymerization catalyst systems. Particularly, theinvention relates to a process for transitioning between an olefinpolymerization reaction utilizing a traditional Ziegler-Natta catalystsystem to an olefin polymerization reaction utilizing a bulky ligandtransition metal metallocene catalyst system and vice-versa.

Metallocenes revolutionized the last decade by developing products thathave improved characteristics compared to traditional Ziegler-Nattacatalyst based products. Metallocene and single site catalyst basedproducts provided: (1) narrower molecular weight distribution, (2)better comonomer incorporation and (3) lower densities compared toconventional Z—N based products. These characteristics provided severaladvantages at the end user level including: (1) impact strength, (2)clarity, (3) organoleptic properties, (4) heat-seal characteristics andmost importantly an opportunity to downgage.

Metallocene-LLDPE has been targeted for mono layer and multi-layer blownfilm and packaging applications. Commercial applications of LLDPE arenotably in the blown and cast film use, such as stretch film, as well ascan liners and heavy duty sacks. It has provided end users with manyadvantages such as: (1) increased packaging speeds due to lower sealinitiation temperature, higher hot tack, and reduced blocking; (2)reduced package failures due to greater toughness and superiorresistance to abuse; (3) improved package artistic due to lower haze andhigher gloss; and (4) improved packaged product quality due to reducedpackage-product interactions, lower odor and extractability, etc. LLDPEfor producing films requires that no gel is formed during the productionof LLDPE.

It is frequently necessary to transition from one type of catalystsystem producing polymers having certain properties and characteristicsto another catalyst system capable of producing polymers of differentchemical and/or physical attributes. Transitioning between similarZiegler-Natta catalyst systems or compatible catalyst systems generallytakes place easily. Compatible catalysts are those catalysts havingsimilar kinetics of termination and insertion of monomer and co-monomer(s) and/or do not detrimentally interact with each other.

However, the process is typically complicated when the catalyst systemsare incompatible or of different types. For example, when transitioningbetween two incompatible catalyst systems such as a Ziegler-Nattacatalyst system and a metallocene catalyst system, it has been foundthat some of the components of the Ziegler-Natta catalyst system act aspoisons to the metallocene catalyst system. Consequently, the componentsof the Ziegler-Natta catalyst system prevent the metallocene catalystsystem from promoting polymerization.

Furthermore, particularly in a continuous transition process, theinteraction between two incompatible catalysts may lead to theproduction of high levels of small particles less than about 120 micronsthat are referred to as “fines”. Fines can induce operability problemsin the reactor and/or fouling and sheeting incidents.

In the past, to accomplish an effective transition between incompatiblecatalysts, the first catalyzed olefin polymerization process was stoppedby various techniques known in the art. The reactor was then emptied,recharged and a second catalyst system was introduced into the reactor.Such catalyst conversions are time consuming and costly because of theneed for a reactor shut-down for an extended period of time duringtransition and the off-grade material.

There have been many attempts to improve the process for transitioningbetween incompatible catalysts.

Naturally, in order to inhibit polymerization of a first incompatiblecatalyst, it is necessary to interrupt catalyst injection into thereactor. Stopping the first catalyst feed into the reactor does notimmediately stop polymerization reactions occurring within the reactorbecause the fluidized bed contains catalyst particles which can stillpolymerize for an extended period of time. Even if one were to allow thepolymerization reactions within the reactor to continue for a period oftime, the catalyst within the reactor would not be completelydeactivated for a considerable period.

Thus, to substantially terminate these polymerization reactions withinthe reactor, polymerization inhibitors or “catalyst killers” areemployed. There are two general types of polymerization inhibitors:reversible catalyst killers and irreversible catalyst killers.Reversible catalyst killers typically initially inhibit catalystactivity and polymerization for a period of time, but, do notirreversibly deactivate the catalyst. In fact, after a period of timeunder normal polymerization conditions the catalysts reactivate andpolymerization will continue. These reversible catalyst killers can beused in any combination or order of introduction in the process.Irreversible catalyst killers irreversibly inactivate a catalyst'sability to polymerize olefins. The use of catalyst killing and/ordeactivating agents is disclosed in U.S. Pat. Nos. 5,442,019, 5,753,786,and 6,949,612 B2 to Agapiou et al., U.S. Pat. No. 5,672,666 to Muhle etal., and U.S. Pat. No. 6,858,684 B2 to Burdett et al.

U.S. Pat. No. 5,672,666 describes a process for transitioning from aZiegler-Natta catalyst to a metallocene catalyst in which a deactivatingagent (CO2) is introduced to the reactor, the reactor is purged toremove any remaining deactivating agent and the metallocene catalyst isintroduced into the reactor in the absence of any scavenger material.U.S. Pat. No. 5,672,666 mentions that substantially all of theactivating and/or scavenging compounds, for example TEAL, are removedprior to the introduction of the metallocene catalyst.

It would be advantageous to provide a catalyst transitioning processwhich ensures the effect of the original catalyst system is eliminated.Further, it would be advantageous to provide a catalyst transitioningprocess without the need for halting the polymerization reaction,emptying the reactor to rid it of the original catalyst system andrestarting the polymerization reaction with another catalyst system. Inaddition, it would be advantageous if the process for transitioningcould reduce the amount of off-grade material produced during thetransition process, reduce the transition time, increase the robustnessand stability of the transition process and avoid the need to open thereactor to charge the seed bed.

It is an object of the present invention to provide a process in whichabove-described and/or other problems are solved.

Accordingly, the present invention provides a process for transitioningfrom a first continuous polymerization reaction in a gas phase reactorconducted in the presence of a first catalyst to a second polymerizationreaction conducted in the presence of a second catalyst in the gas phasereactor wherein the first and second catalysts are incompatible, theprocess comprising:

(a) discontinuing the introduction of the first catalyst from a firstcatalyst feeding system into the gas phase reactor;

(b) introducing a catalyst killer to at least partially deactivate thefirst catalyst in the reactor and

(c) introducing into the reactor a second catalyst from a secondcatalyst feeding system separate from the first catalyst feeding system.

For the purposes of this patent specification and appended claims, theterm “incompatible catalysts” are understood as those that satisfy oneor more of the following: 1) those catalysts that in each other'spresence reduce the productivity of at least one of the catalysts bygreater than 50%; 2) those catalysts that under the same reactiveconditions one of the catalysts produces polymers having a molecularweight (Mw) greater than two times higher than any other catalyst in thesystem; and 3) those catalysts that differ in comonomer incorporation orreactivity ratio under the same conditions by more than about 30%

Productivity is herein understood as kg of product per kg of catalystover a certain period of time. Mw is herein understood as the weightaverage molecular weight as measured using SEC (Size ExclusionChromatrography using 1,2,4-trichlorobenzene as an eluent, andcalibrated using linear polyethylene standards. The comonomerincorporation is measured by the analytical temperature rising elutionfractionation (aTREF) conducted according to the method described inU.S. Pat. No. 4,798,081 and Wilde, L.; Ryle, T. R.; Knobeloch, D. C;Peat, LR.; Determination of Branching Distributions in Polyethylene andEthylene Copolymers, J. Polym. ScL, 20, 441-455 (1982), which areincorporated by reference herein in their entirety. The composition tobe analyzed is dissolved in 1,2-dichlorobenzene of analytical qualityfiltrated via 0.2 μm filter and allowed to crystallize in a columncontaining an inert support (Column filled with 150 μm stainless steelbeans (volume 2500 μL) by slowly reducing the temperature to 20° C. at acooling rate of 0.1° C./min. The column is equipped with an infrareddetector. An ATREF chromatogram curve is then generated by eluting thecrystallized polymer sample from the column by slowly increasing thetemperature of the eluting solvent (1,2-dichlorobenzene) from 20 to 130°C. at a rate of 1° C./min.

The instrument used may be Polymer Char Crystaf-TREF 300.

Stabilizers: 1 g/L Topanol+1 g/L Irgafos 168

Sample: approx. 70 mg in 20 mL

Sample volume: 0.3 mL

Pump flow: 0.50 mL/min

The software from the Polymer Char Crystaf-TREF-300 may be used togenerate the spectra.

The present invention is based on the realization that even a traceamount of a catalyst can be poisonous to an incompatible catalyst and nocontact should be made between incompatible catalysts not only in thereactor but also in the catalyst feeding system. A catalyst is fed froma catalyst feeding system comprising for example a catalyst supplyvessel and an injection tube connected to the catalyst supply vessel andthe reactor. The catalyst feeding system above may optionally alsocomprise a pump. Another example of suitable catalyst feeding system cancomprise a storage chamber, a metering device and an intermediatechamber, through which an inert carrier gas is released by afast-opening valve to sweep the powder to the reactor (such a system isdescribed for example in U.S. Pat. No. 4,774,299). A further example ofsuitable catalyst feeding system can use a compressed gas to deliver thecatalyst (such a system is described for example in U.S. Pat. No.3,790,036). Another example of suitable catalyst feeding system can workthrough for steps of subdividing, intercepting, exposing and flashingthe catalyst by opening and closing of a catalyst feed line (such asystem is described for example in JP 49-17426). Other examples ofcatalyst feeder systems are described in EP 0596111, EP 0961784, U.S.Pat. Nos. 4,610,574, 5,195,654, 5,209,607, 5,738,249 or WO 9201722. Itwas found that, even when the catalyst (and other poisonous componentsderived from the remaining catalysts) is not present in the reactor, atrace amount of the catalyst sufficient to be poisonous to the secondcatalyst still remains in the injection tube which cannot be removed bypurging.

The polymerization catalysts used in the present invention are solidcatalysts. The solid polymerization catalyst may be fed to the reactoras a suspension in a solvent, for example a hydrocarbon solvent or thelike, or in an inert gas, such as nitrogen. The solid polymerizationcatalyst may also be injected into the reactor as a dry catalyst. Atrace amount of remaining catalyst was found not to have adverse effecton the density and the melt index. Purging is sufficient to remove thecatalyst to the level which does not influence the density and the meltindex. The present inventors surprisingly found that a trace amount ofremaining catalyst remaining in the catalyst feeding system leads to anexcessive gel content, which makes the obtained polymer unsuitable forcertain applications, such as LLDPE for film applications.

The deactivation of the catalyst remaining in the reactor has previouslybeen studied in detail. Examples of these studies are found in U.S. Pat.No. 6,949,612, US 20050059784, WO 2004060931, U.S. Pat. Nos. 5,747,612,5,442,019, 5,672,665, 5,753,786. None of these prior art documentsmention the effect of the trace amount of incompatible catalyst and thepossibility of the catalyst remaining in the catalyst feeding systemeven after intensive purging.

U.S. Pat. No. 5,672,666 describes a process for transitioning from aZiegler-Natta catalyst to a metallocene catalyst in which a deactivatingagent is introduced to the reactor and the reactor is purged before theintroduction of the metallocene catalyst. U.S. Pat. No. 5,672,666mentions that substantially all of the activating and/or scavengingcompounds, for example TEAL, are removed prior to the introduction ofthe metallocene catalyst. U.S. Pat. No. 5,672,666 further mentions thatit is important that if a common catalyst feeder system is used it toobe substantially free of any residual catalyst.

The present inventors surprisingly found that using a common catalystfeeder system cleaned by purging can only lead to a system which issubstantially free of the residual catalyst which is satisfactory interms of density and melt index, but not gel content. For transitioningto obtain polyethylene having also a desired low gel content, a catalystfeeder substantially free of residual catalyst achieved by purging isinsufficient, but a catalyst feeder completely free of residual catalystis required. Accordingly, the present invention provides the use of twoseparate catalyst feeders. U.S. Pat. No. 5,672,666 does not mention thatseparate catalyst feeders have to be used since the catalyst feeder mustbe completely free of residual catalyst and that a common catalystfeeder system made substantially free of residual catalyst e.g. bypurging is insufficient.

The problem caused by the remaining first catalyst can also be avoidedby physically cleaning the first catalyst feeding system. This allowsthe use of the first catalyst feeding system for the second catalystfeeding system. However, the physical cleaning of the catalyst feedingsystem typically takes 6-8 hours. Instead of the time consuming physicalcleaning, two separate catalyst feeders are used for two incompatiblecatalysts in the process according to the invention.

The first catalyst may be fed as a dry catalyst and the second catalystmay be fed as a dry catalyst.

The first catalyst may be fed as a dry catalyst and the second catalystmay be fed as a suspension in a solvent.

The first catalyst may be fed as as a suspension in a solvent and thesecond catalyst may be fed as a dry catalyst.

The first catalyst may be fed as as a suspension in a solvent and thesecond catalyst may be fed as a suspension in a solvent.

In particular, the first catalyst may be a Ziegler-Natta catalyst and befed as a suspension in a solvent and the second catalyst may be ametallocene catalyst and be fed as a dry catalyst.

In particular, the first catalyst may be a Ziegler-Natta catalyst and befed as a dry catalyst and the second catalyst may be a metallocenecatalyst and be fed as a dry catalyst.

For the purposes of this patent specification and appended claims theterms “catalysts” and “catalyst systems” are used interchangeably.

Polymerization

The first polymerization reaction and the second polymerization reactionmay be a continuous polymerization of one or more α-olefin monomers ofwhich at least one is ethylene or propylene. Preferred α-olefin monomersinclude for example α-olefins having from 4 to 8 carbon atoms. However,small quantities of α-olefin monomers having more than 8 carbon atoms,for example 9 to 18 carbon atoms, such as for example a conjugateddiene, can be employed if desired. Thus it is possible to producehomopolymers of ethylene or propylene or copolymers of ethylene and/orpropylene with one of more α-olefin monomers having from 4 to 8 α-olefinmonomers. Preferred α-olefin monomers include but are not limited tobut-1-ene, isobutene, pent-1-ene, hex-1-ene, hexadiene, isoprene,styrene, 4-methylpent-1-ene, oct-1-ene and butadiene. Examples ofα-olefin monomers having more than 8 carbon atoms that can becopolymerized with an ethylene and/or propylene monomer, or that can beused as partial replacement for α-olefin monomers having from 4 to 8α-olefin monomers include but are not limited to dec-1-ene andethylidene norbornene.

When the process of the invention is used for the copolymerization ofethylene and/or propylene with α-olefin monomers, the ethylene and/orpropylene preferably is used as the major component of the copolymer.For example, the amount of ethylene and/or propylene present in thecopolymer is at least 65% by weight, for example at least 70% by weight,for example at least 80% by weight based on the total copolymer.

With ‘continuous polymerization of one or more α-olefins’ or ‘continuouspreparation of polyolefin’ is meant herein that one or more α-olefinmonomers of which at least one is ethylene or propylene are fed to thereactor and polyolefin thus produced is (semi)-continuously withdrawnthrough a polymer discharge system connected to the reactor.

The continuous polymerization of one or more α-olefin monomers willproduce polyolefins in the form of particles, herein also referred to as‘polyolefin’. Examples of polyolefins which may be produced, include awide variety of polymers, for example polyethylene, for example linearlow density polyethylene (LLDPE), which may for example be prepared fromethylene and but-1-ene, 4-methylpent-1-ene or hex-1-ene, high densitypolyethylene (HDPE), which may for example be prepared from ethylene orfrom ethylene with a small portion of an α-olefin monomer having from 4to 8 carbon atoms, for example but-1-ene, pent-1-ene, hex-1-ene or4-methylpent-1-ene. Other examples include but are not limited toplastomers, elastomers, medium density polyethylene, polypropylenehomopolymers and polypropylene copolymers, including random copolymers,and block or multi-block copolymer and ethylene propylene rubber (EPR).

Preferably, in the process of the invention, the polyolefin produced isa polyethylene, more preferably a linear low density polyethylene.

Fluidized Bed

The process of this invention can be used in any gas phasepolymerization process in a gas phase reactor. The gas phase reactor maybe any reactor suitable for gas phase polymerizations and may e.g. bevertically, horizontally mechanically agitated reactor or a fluidizedbed reactor. A gas phase polymerization process in a fluidized bedreactor is preferred. In a typical continuous gas fluidized bedpolymerization process for the production of polymer from monomer, agaseous stream comprising monomer is passed through a fluidized bedreactor in the presence of a catalyst under reactive conditions.

Gas fluidized bed polymerization plants generally employ a continuousgas cycle. In one part of the cycle, in a reactor a cycling gas streamis heated by the heat of polymerization. This heat is removed in anotherpart of the cycle by a cooling system external to the reactor. In oneembodiment the cycle gas stream is cooled to form a gas and a liquidphase mixture that is then introduced into the reactor. A polymerproduct is withdrawn from the reactor. For a detailed description of agas phase process see U.S. Pat. Nos. 4,543,399 and 4,588,790 hereinfully incorporated by reference

Using a fluidized bed polymerization process substantially reduces theenergy requirements as compared to other polymerization processes andmost importantly reduces the capital investment required to run such apolymerization process. In preferred embodiments, the fluidized bed ismaintained in a fluidized condition during the process of thisinvention.

There are many types of fluidized bed reactors, among which a bubblingfluidized bed reactor, a circulating fluidized bed reactor, an annularfluidized bed reactor, a multi-zone fluidized bed reactor and a flashreactor.

The process according to the invention is preferably performed in amulti-zone fluidized bed reactor.

With ‘fluidized bed’ as used herein is meant that an amount of solidparticles (in this case preferably the solid catalyst and/or the solidcatalyst to which the monomer is attached) in a solid/fluid mixture actsas a fluid. This can be achieved by placing the amount of solidparticles under appropriate conditions, for instance by the introductionof fluid through the solid particles at a high enough velocity tosuspend the solid particles and causing them to behave as a fluid.

An example of a process using a fluidized bed for producing polyolefinsis disclosed in U.S. Pat. No. 4,882,400. Other examples of processesusing a fluidized bed for producing polyolefins are described in, forexample, U.S. Pat. Nos. 3,709,853; 4,003,712; 4,011,382; 4,302,566;4,543,399; 4,882,400; 5,352,749; 5,541,270; 7,122,607, and 7,300,987.The bottom of a fluidized bed reactor (FBR) can for example comprise aninlet connected to a feeder for the reaction composition such asethylene, nitrogen (N2), hydrogen (H2), comonomer, tri-isobutylamine(TIBAL)-amine, and triethylaluminium (TEAL). The middle zone in thereactor above the distribution plate comprises an inlet for thepolymerization catalyst that can be fed to the reactor in combinationwith nitrogen (N2). The middle zone of the reactor also comprises anoutlet to the product discharge tank. The top zone of the reactorcomprises an outlet for a top recycle stream, wherein the outlet for thetop recycle stream is connected to an inlet of the compressor. Thecompressor comprises an outlet for compressed fluids and the outlet ofthe compressor is connected to an inlet for compressed fluids of thecooling unit. The cooling unit comprises an outlet for providing abottom recycle stream, which outlet of the cooling unit is connected tothe inlet at the bottom of the reactor.

An example of a multi-zone fluidized bed reactor (FBR) system is shownin FIG. 1. The multi-zone reactor of this example is a multi-zonereactor operable in condensed mode, which multi-zone reactor comprises afirst zone, a second zone, a third zone, a fourth zone and adistribution plate,

wherein the first zone is separated from the second zone by thedistribution plate, wherein the multi-zone reactor is extended in thevertical direction wherein the second zone of the multi-zone reactor islocated above the first zone and wherein the third zone of themulti-zone reactor is located above the second zone, and wherein thefourth zone of the multi-zone reactor is located above the third zonewherein the second zone contains an inner wall, wherein at least part ofthe inner wall of the second zone is either in the form of a graduallyincreasing inner diameter or a continuously opening cone, wherein thediameter or the opening increases in the vertical direction towards thetop of the multi-zone reactorwherein the third zone contains an inner wall, wherein at least part ofthe inner wall of the third zone is either in the form of a graduallyincreasing inner diameter or a continuously opening cone, wherein thediameter or the opening increases in the vertical direction towards thetop of the multi-zone reactorwherein the largest diameter of the inner wall of the third zone islarger than the largest diameter of the inner wall of the second zone.

The FBR of this example can operate in a so-called “condensing mode” or“condensed mode” which is effective for removal of the heat producedduring the exothermic polymerization. In this mode, heat removal isachieved by cooling the gaseous recycle stream to a temperature belowits dew point, resulting in the condensation of at least a part of therecycle stream to form a bottom recycle stream containing liquid andgas. The thus formed bottom recycle stream is then introduced into thefluidized bed polymerization reactor, where the liquid portion willvaporize upon exposure to the heat of the reactor, which vaporizationwill remove heat from the reactor and enables feeding of one or morevery highly active catalysts. Details of the FBR which operates in acondensing mode are further described in Application no. EP 13195141.0,incorporated herein by reference.

BRIEF DESCRIPTION OF THE FIGURE

The figure illustrates an FBR system comprising a multi-zone reactor(8), a compressor (400) and a cooling unit (5).

The multi-zone reactor (8) of this example is extended in the verticaldirection and comprises four reaction zones (1), (2), (3) and (4). Zone(4) can preferably be located above zone (3), zone (3) can be locatedabove zone (2) and zone (2) can located above zone (1) in the verticaldirection toward the top of the reactor.

The first zone (1) comprises a first inlet for receiving a bottomrecycle stream (10) and the first zone (1) is separated from the secondzone (2) by a distribution plate (6). The second zone (2) comprises afirst inlet for receiving a solid polymerization catalyst (20). Thethird zone (3) comprises a first outlet for providing polyolefin (30).This outlet can also be located in the second zone (2). At least one ofthe second zone (2) or the third zone (3) can comprise at least onesection where the inner wall of the reactor is either in the form of agradually increasing inner diameter or a continuously opening cone inthe vertical direction towards the top of the reactor. Here both thesecond zone (2) and the third zone (3) comprise such sections designatedrespectively by 2A and 3A. In the second zone (2), at least one sectionwhere the inner wall of the reactor is either in the form of a graduallyincreasing inner diameter or a continuously opening cone in the verticaldirection towards the top of the reactor (2A) can preferably be locatedimmediately above the distribution plate (6). Immediately above thedistribution plate (6) can thereby preferably mean so that pooling ofliquid can be reduced or avoided. Moreover, at least one of the secondzone (2) or the third zone (3) can comprise at least one section wherethe inner wall of the reactor is either in the form of a cylinder. Hereboth the second zone (2) and the third zone (3) comprise such sectionsdesignated respectively by 2B and 3B. The fourth zone (4) comprises afirst outlet for a top recycle stream (40) which is connected to a firstinlet of the compressor (400) via a first connection means (AA). Thefourth zone is thereby a disengagement zone, which may be designed sothat polymer particles preferably do not reach that zone or do not stayas little as possible in that zone but rather return to the third zone(3) or the second zone (2), especially for example to allow avoiding theclogging of the compressor (400). The connection means (AA) comprise afirst inlet for receiving a feed (60).

The compressor (400) comprises a first outlet for compressed fluids (50)which is connected to a first inlet for compressed fluids of the coolingunit (5) via a second connection means (BB). The second connection means(BB) comprise an inlet for receiving a feed (70). The cooling unit (5)comprises a first outlet for providing the bottom recycle stream (10)which is connected to the first inlet of the first zone (1).

The FBR system may further comprise a polymer withdrawal system, apolymer degassing system and a vent gas recovery system (not shown inFIG. 1). The outlet for the recovered components (in liquid form) (80)from the vent gas recovery system may be transported to the first inlet(70) of the second connection means (BB) by means of pump (7).

This system can suitably be used for a process for continuouspolymerization comprising

-   -   supplying the second zone (2) with a solid polymerization        catalyst using the first inlet for receiving the solid        polymerization catalyst (20)    -   supplying a feed (60) comprising an α-olefin monomer to the        first connection means (AA)    -   optionally supplying a feed (70) comprising condensable inert        components to the second connection means (BB)    -   withdrawing the polyolefin (30) using the first outlet of the        second zone (2) and/or the third zone (3) and    -   circulating fluids from the first outlet of the fourth zone (4)        to the first inlet of the first zone        wherein the fluids are circulated by    -   compressing the feed (60) and the top recycle stream (40) using        the compressor (400) to form the compressed fluids (50)    -   subsequently cooling the compressed fluids (50) using the        cooling unit (5) to below the dew point of the compressed fluids        to form the bottom recycle stream (10) and    -   feeding the bottom recycle stream (10) to the first zone of the        multi-zone reactor (8) via the inlet for receiving the bottom        recycle stream of the first zone, and    -   wherein the superficial gas velocity in this process is in the        range of 0.5 to 5 m/s.

The feed (60) comprises a chain transfer agent, for example hydrogen andmay further comprise gaseous α-olefin monomers and insert gaseouscomponents, for example nitrogen.

The feed (70) comprises condensable inert components, for example acondensable inert component selected from the group of alkanes having 4to 20 carbon atoms, preferably 4 to 8 carbon atoms, and mixturesthereof, for example propane, n-butane, isobutene, n-pentane,isopentane, neopentane, n-hexane, isohexane or other saturatedhydrocarbons having 6 C-atoms, n-heptane, n-octane and other saturatedhydrocarbons having 7 or 8 C-atoms and any mixtures thereof; and mayfurther comprise condensable α-olefin monomers, α-olefin comonomersand/or mixtures thereof.

The above FBR system has the advantage that introduction of higheramounts of liquid is allowed without causing destabilization of thefluidized bed.

Catalysts

While in the preferred embodiment the process of the inventionspecifically addresses transitioning between a traditional Ziegler-Nattacatalyst and a metallocene catalyst, it is within the scope of thisinvention that the process of the invention would apply to anytransition between incompatible catalysts. For example, transitioningbetween a traditional Ziegler-Natta catalyst and a chromium catalyst ortransitioning between a chromium catalyst and a metallocene catalyst oreven transitioning between a traditional Ziegler-Natta titanium catalystto a Ziegler-Natta vanadium catalyst. This invention contemplates thatthe direction of transitioning between incompatible catalysts is notlimiting, however, it is preferred that the process of the inventiontransition from any other catalyst incompatible with a metallocenecatalyst.

Traditional Ziegler-Natta catalysts typically in the art comprise atransition metal halide, such as titanium or vanadium halide, and anorganometallic compound of a metal of Group 1, 2 or 3, typicallytrialkylaluminum compounds, which serve as an activator for thetransition metal halide. Some Ziegler-Natta catalyst systems incorporatean internal electron donor which is complexed to the alkyl aluminum orthe transition metal. The transition metal halide may be supported on amagnesium halide or complexed thereto. This active Ziegler-Nattacatalyst may also be impregnated onto an inorganic support such assilica or alumina. For the purposes of this patent specificationchromocene catalysts, for example, described in U.S. Pat. No. 4,460,755,which is incorporated herein by reference, are also considered to betraditional Ziegler-Natta catalysts. For more details on traditionalZiegler-Natta catalysts, see for example, U.S. Pat. Nos. 3,687,920,4,086,408, 4,376,191, 5,019,633, 4,482,687, 4,101,445, 4,560,671,4,719,193, 4,755,495, 5,070,055 all of which are herein incorporated byreference.

The metallocene catalyst is preferably a metallocene catalyst of thegeneral formula I below

wherein:M is a transition metal selected from the group consisting oflanthanides and metals from group 3, 4, 5 or 6 of the Periodic System ofElements; M is preferably selected from the group consisting of Ti, Zrand Hf with Zr being most preferred.Q is an anionic ligand to M,k represents the number of anionic ligands Q and equals the valence of Mminus two divided by the valence of the anionic Q ligandR is a hydrocarbon bridging group, such as alkyl. R preferably containsat least one sp2-hybridised carbon atom that is bonded to the indenylgroup at the 2-position.Z and X are substituents.

In another preferred embodiment the metallocene catalyst is of thegeneral formula II below

wherein:M is a transition metal selected from the group consisting oflanthanides and metals from group 3, 4, 5 or 6 of the Periodic System ofElements; M is preferably selected from the group consisting of Ti, Zrand Hf with Zr being most preferred.Q is an anionic ligand to M,k represents the number of anionic ligands Q and equals the valence of Mminus two divided by the valence of the anionic Q ligandR is a hydrocarbon bridging group, such as alkyl. R preferably containsat least one sp2-hybridised carbon atom that is bonded to the indenylgroup at the 2-position.Z and X are substituents.

Bridging group R in the metallocene catalysts of general formula's I andII above preferably contains at least one aryl group. For example, thearyl group may be a monoaryl group such as phenylene or naphthalene or abiaryl group, such as biphenylidene or binaphthyl. Preferably thebridging group R stands for an aryl group, preferably R stands for aphenylene or biphenylidene group. The bridging group R is connected tothe indenyl groups via a sp2 hybridised carbon atom, for example aphenylene group may be connected via the 1 and the 2 position, abiphenylene group may be connected via the 2 and 2′-position, anaphthalene group may be connected via the 2 and 3-position, a binapthylgroup may be connected via the 2 and 2′-position. Preferably R standsfor a phenylene group that is connected to the indenyl groups via the 1and the 2 position. R may be 2,2′-biphenylene.

The substituents X in formulas I and II above may each separately behydrogen or a hydrocarbon group with 1-20 carbon atoms (e.g. alkyl,aryl, aryl alkyl). Examples of alkyl groups are methyl, ethyl, propyl,butyl, hexyl and decyl. Examples of aryl groups are phenyl, mesityl,tolyl and cumenyl. Examples of aryl alkyl groups are benzyl,pentamethylbenzyl, xylyl, styryl and trityl. Examples of othersubstituents are halides, such as chloride, bromide, fluoride andiodide, methoxy, ethoxy and phenoxy. Also, two adjacent hydrocarbonradicals may be connected with each other in a ring system. X may alsobe a substituent which instead of or in addition to carbon and/orhydrogen may comprise one or more heteroatoms from group 14, 15 or 16 ofthe Periodic System of Elements. Examples of such a heteroatomcontaining substituents are alkylsulphides (like MeS—, PhS—,n-butyl-S—), amines (like Me2N—, n-butyl-N—), Si or B containing groups(like Me3Si— or Et2B—) or P-containing groups (like Me2P— or Ph2P—).Preferably the X substituents are hydrogen.

The substituents Z in formulas I and II above may each separately be asubstituent as defined above for substituent X. Z1 and Z2 substituentscan together with the X1 and X4 substituents form a second bridge thatconnects the indenyl group with the cyclopentadienyl group in theindenyl compound.

Examples of metallocene catalysts for use in the present invention are[ortho-bis(4-phenyl-2-indenyl)-benzene]zirconiumdichloride,[ortho-bis(5-phenyl-2-indenyl)-benzene]zirconiumdichloride,[ortho-bis(2-indenyl)benzene]zirconiumdichloride,[ortho-bis(2-indenyl)benzene]hafniumdichloride,[ortho-bis(1-methyl-2-indenyl)-benzene]zirconiumdichloride,[2.2′-(1.2-phenyldiyl)-1.1′-dimethylsilyl-bis(indene)]zirconiumdichloride,[2,2′-(1,2-phenyldiyl)-1, bis(indene)]zirconiumdichloride,[2,2′-(1.2-phenyldiyl)-1.1′-(1.2-ethanediyl)-bis(indene)]zirconiumdichloride,[2.2′-bis(2-indenyl)biphenypirconiumdichloride and[2,2′-bis(2-indenyl)biphenyl]hafniumdichloride.

The metallocene catalyst preferably contains zirconium as metal group M.The zirconium amount in the catalyst composition is preferably in therange of 0.02-1 wt %, preferably 0.15-0.30 wt % based on the catalystcomposition.

The metallocene catalyst may be supported on a support, optionally witha catalyst activator and optionally a modifier. The second catalyst ispreferably a metallocene catalyst composition comprising a supportcontaining a metallocene catalyst, a catalyst activator and a modifierdescribed in EP2610269, incorporated herein by reference. Such catalystcomposition has an advantage that reactor fouling is reduced. It wasobserved that such catalyst composition was particularly sensitive tothe gelling problem when common catalyst feeder was used.

The term “catalyst activator” as used herein is to be understood as anycompound which can activate the single-site catalyst so that it iscapable of polymerisation of monomers, in particular olefins. Preferablythe catalyst activator is an alumoxane, a perfluorophenylborane and/or aperfluorophenylborate, preferably alumoxane, more preferablymethylaluminoxane and/or modified methylaluminoxane.

The support in the catalyst composition of the present invention can bean organic or inorganic material and is preferably porous. Examples oforganic material are cross-linked or functionalized polystyrene, PVC,cross-linked polyethylene. Examples of inorganic material are silica,alumina, silica-alumina, inorganic chlorides such as MgCl₂, talc andzeolite. Mixtures of two or more of these supports may be used. Thepreferred particle size of the support is from 1 to 120 micrometres,preferably of from 20 to 80 micrometres and the preferred averageparticle size is from 40 to 50 micrometres. The preferred support issilica. The pore volume of the support is preferably of from 0.5 to 3cm³/g. The preferred surface area of the support material is in therange of from 50 to 500 m²/g. The silica used in this invention ispreferably dehydrated prior to being used to prepare the catalystcomposition.

Preferably, the modifier is the reaction product of an aluminum compoundof general formula (1)

and an amine compound of general formula (2)

whereinR1 is hydrogen or a branched or straight, substituted or unsubstitutedhydrocarbon group having 1-30 carbon atoms,R2 and R3 are the same or different and selected from branched orstraight, substituted or unsubstituted hydrocarbon groups having 1-30carbon atoms andR4 is hydrogen or a functional group with at least one active hydrogenR5 is hydrogen or a branched, straight or cyclic, substituted orunsubstituted hydrocarbon group having 1-30 carbon atoms,R6 is a branched, straight or cyclic, substituted or unsubstitutedhydrocarbon group having 1-30 carbon atoms.

In a preferred embodiment of the invention the amounts of aluminumcompound and amine compound are selected such that in the modifier themolar ratio of Al to N is in the range of 1:3 to 5:1, preferably 1:2 to3:1, more preferably 1:1.5 to 1.5:1. Within this range a goodcombination of technical effects of the present invention can beobtained. If the molar ratio of Al to N is below 1:3 then fouling and/orsheeting may occur, whereas if the molar ratio of Al to N is above 5:1catalyst productivity decreases, i.e. the amount of polymer produced pergram of catalyst decreases. The most preferred molar ratio is 1:1.

In the compound of general formula (2), R4 is a hydrogen or a functionalgroup with at least one active hydrogen, R5 is hydrogen or a branched,straight or cyclic, substituted or unsubstituted hydrocarbon grouphaving 1-30 carbon atoms, R6 is a branched, straight or cyclic,substituted or unsubstituted hydrocarbon group having 1-30 carbon atoms(carbon atoms of the substituents included). The branched, straight orcyclic, substituted or unsubstituted hydrocarbon group having 1-30carbon atoms is preferably an alkyl group having 1-30 carbon atoms, forexample an alkyl group having 1-30 carbon atoms, for example a straight,branched or cyclic alkyl, an aralkyl group having 1-30 carbon atoms oran alkaryl group having 1-30 carbon atoms.

The amine compound used in the reaction to prepare the modifier may be asingle amine compound or a mixture of two or more different aminecompounds.

The amine compound used for preparing the modifier of the presentinvention preferably has a hydrocarbon group of at least eight carbonatoms, more preferably at least twelve carbon atoms, for example analkyl group of 1 to fifteen carbon atoms. The amine compound may be aprimary, secondary or tertiary amine. The amine compound is preferably aprimary amine.

In an embodiment of the present invention the amine compound is selectedfrom the group consisting of octadecylamine, ethylhexylamine,cyclohexylamine, bis(4-aminocyclohexyl)methane, hexamethylenediamine,1,3-benzenedimethanamine,1-amino-3-aminomethyl-3,5,5-trimethylcyclohexane and6-amino-1,3-dimethyluracil.

The aluminum compound used in the reaction to prepare the modifier maybe a single aluminum compound or a mixture of two or more differentaluminum compounds. R1, R2 and R3 may each independently stand for abranched or straight, substituted or unsubstituted hydrocarbon grouphaving 1-30 carbon atoms, for example may each independently stand foran alkyl, preferably R1, R2 and R3 all stand for an alkyl, morepreferably R1, R2 and R3 are the same.

The aluminum compound of the present invention is preferably atrialkylaluminum (R1=R2=R3=alkyl or a dialkylaluminumhydride(R1=hydrogen, R2=R3=alkyl). In an embodiment of the present inventionthe aluminum compound is selected from the group consisting of oftri-methylaluminum, tri-ethylaluminum, tri-propylaluminum,tri-butylaluminum, tri-isopropylaluminum tri-isobutylaluminum, ordi-methylaluminumhydride, di-ethylaluminumhydride,di-propylaluminumhydride, di-butylaluminumhydride,di-isopropylaluminumhydride, di-isobutylaluminumhydride. These materialsare readily available and have good reactivity with amines. An alkyl asused herein will be understood by the skilled person as meaning ahydrocarbon group that contains only carbon and hydrogen atoms and isderived from alkanes such as methane, ethane, propane, butane, pentane,hexane etc. The alkyl may be branched, straight or cyclic. PreferablyR1, R2 and R3 may each independently stand for a straight or branchedalkyl.

In a preferred embodiment the aluminum compound is a trialkylaluminumand the amine compound is a primary amine, preferably the amine compoundis selected from the group consisting of octadecylamine,ethylhexylamine, cyclohexylamine, bis(4-aminocyclohexyl)methane,hexamethylenediamine, 1,3-benzenedimethanamine,1-amino-3-aminomethyl-3,5,5-trimethylcyclohexane and6-amino-1,3-dimethyluracil.

Preferably, the modifier is the reaction product of cyclohexylamine andtri-isobutylaluminum.

In some embodiments, the modifier is an amine compound of generalformula (3)

where R7 is hydrogen or a linear or branched alkyl group of from 1 to 50carbon atoms;R8 is a hydroxy group of a (CH₂)_(x) radical and where x is an integerfrom 1 to 50. An example of these surface modifiers includescommercially available Atmer 163. It was observed that such catalystcomposition was particularly sensitive to the gelling problem whencommon catalyst feeder was used.

The surface modifier may be selected from at least one of the group ofcompounds represented by the following chemical formula:C₁₈H₃₇N(CH₂CH₂OH)₂, C₁₂H₂₅N(CH₂CH₂OH)₂ and(CH₃(CH₂)₇(CH)₂(CH₂)₇OCOCH₂(CHOH)₄CH₂OH. The surface modifier may be asorbital monooleate compound or a tertiary ethoxylated amine.

Step (a)

Step (a) is preferably performed in such a way that the ratio betweenthe first catalyst and a co-catalyst of the first catalyst ismaintained. Step (a) may generally be performed by decreasing the amountof the first catalyst and its co-catalyst over a period of 1-4 hours.

After the introduction of the first catalyst and its co-catalyst isstopped, the reactor gas composition for the first polymerization ispreferably maintained for a period of time, e.g. 1-4 hours. This allowsthe consumption of the co-catalyst and gradual reduction in theproduction rate.

Conventionally, gas phase polymerization processes typically runcontinuously, therefore the temperature of the fluidized bed reactor iscontrolled to an essentially isothermal level through continuouslyremoving the heat of polymerization by circulating the gas exiting fromthe fluidized bed to a condenser/heat exchanger outside the reactor andrecirculating the cooled gas stream back into the reactor. When thetemperature of the recirculating stream introduced or recycled into thefluidized bed polymerization reactor is above the dew point temperature,substantially no liquid is present. This process is known as the “drymode” process. One method to maximize the ability of heat removal is,throughout the operation, to reduce to the lowest possible value thetemperature of the gaseous feed stream into the reactor.

According to the “condensed mode” process a two phase mixture comprisingliquid and gas is used into the fluidized bed as a fluidizing medium,the liquid portion of which vaporizes when it is exposed to the heat ofthe reactor. Fluid can be formed by cooling the recycle stream withdrawnfrom the reactor below the dew point temperature, thereby converting aportion of the gas into a liquid, and the cooled recycle stream can thenbe reintroduced into the fluidized bed polymerization reactor. Theobjective here is to take advantage of the cooling effect brought aboutby the vaporization, i.e., by bringing the temperature of the fluidizedbed down to a point where degradation of the polymer and the catalystcan be avoided and agglomeration of the polymer and chunking can beprevented. The liquid phase/portion is provided by a portion of therecycle gases, which includes monomers and low boiling liquidhydrocarbons, inert to the reaction conditions needed forpolymerization, and condensation. Condensed mode fluidized bed reactorpolymerization processes are disclosed in for example in U.S. Pat. Nos.4,543,399 and 4,588,790. These publications describe the introduction ofan inert liquid into the recycle stream to increase the dew pointtemperature of the recycle stream and allow the process to operate atlevels of up to 17.4% liquid by weight, based on the total weight of thecooled recycle stream. A condensed mode process is advantageous becauseits ability to remove greater quantities of heat generated bypolymerization increases the polymer production capacity of a fluidizedbed polymerization reactor. A common liquid hydrocarbon used in theliquid phase/portion is isopentane, which boils at about 27° C., andconsequently becomes a vapor in the recycle line in view of the heatpresent in the recycle gases. The recycle gases leave the reactor, arecooled, and then condensed to the extent that a vapor phase/portion andliquid phase/portion are formed. The velocity of the recycled gas/liquidmixture should be sufficient to support the fluidized bed, but slowenough to avoid excessive entrainment of fines. The cooling capacityshould be sufficient to improve the production rate in terms ofspace/time/yield.

“Super condensed mode” fluidized bed reactor polymerization processesoperate with above 17.4% liquid by weight in the cooled recycle streamas described for example in U.S. Pat. No. 5,352,749. These must beconfined under certain more specific and restrictive conditions within alimited and known range of operating conditions to avoid destabilizingthe fluidized bed, thereby halting the process.

In the cases where the first polymerization process is operated in acondensed mode or a supercondensed mode, then a process transitioning isperformed from the condensed mode or the supercondensed mode to the ‘drymode’. This can also be done in step (a) and/or thus preferably forexample before step (b).

Moreover, the fluidized bed reactor may be subjected to a “mini-kill” ora “partial-kill” in which a reversible catalyst killer, preferably CO,is introduced to render the first catalyst inactive, or in other words,incapable of polymerization (even temporary), for example in step (a).Reversible catalyst killer may thereby mean that in absence and/or verylow concentrations (for example below 0.1 ppm) of the reversiblecatalyst killer and/or after a certain time the activity of the catalystcan be restored. This can allow a fast process transitioning fromcondensed mode to dry mode. Typically, the reversible catalyst killer,especially for example CO, may injected to the reactor, where itsconcentrations inside the reactor does for example not exceed 20 ppm ofthe cycle gas flow composition. Preferably the concentration of thereversible catalyst killer inside the reactor can be for example from0.1 to 10 ppm, preferably from 0.1 to 5 ppm, more preferably from 0.1 to3 ppm.

After the introduction of the desired amount of reversible catalystkiller, especially for example CO to the reactor, the reactor can bekept on hold for a short period to ensure the “partial kill”. At leastone reversible catalyst killer can thereby be used for example before,after or together with at least one irreversible catalyst killer.Preferably, at least one reversible catalyst killer can be used (forexample in step (a)) before an irreversible catalyst killer, such asespecially for example cyclohexylamine, is used (for example in step(b)).

Subsequently, product withdrawal can be stopped and/or the polymerdischarge system is separated from the product purge bin and the ventrecovery system, preferably in step (a) and/or thus preferably forexample before step (b).

There are various techniques and systems for removing volatilehydrocarbons from polymers. See, for example, U.S. Pat. Nos. 4,197,399,3,594,356, and 3,450,183, in which a columnar (or straight cylindrical)vessel is used as a purger, referred to as a polymer purge bin, orproduct purge bin. U.S. Pat. No. 4,372,758 discloses a degassing orpurging process for removing hydrocarbons, such as alkenes, from solidolefin polymers. These techniques and systems can be used for/as productpurge bin to remove volatile hydrocarbons from polymers. The purgingprocess generally comprises conveying the solid polymer (e.g., ingranular form) to a polymer purge bin and contacting the polymer in thepurge bin with a countercurrent gas purge stream to strip away thehydrocarbon gases which are evolved from the polymer. Most commonly, thewhole purging is done with an inert gas such as nitrogen. However, it isalso possible to use a light hydrocarbon rich gas to strip the heavierhydrocarbons in a first stage and then use an inert gas in a secondstage for the comparatively easy task of stripping the lighthydrocarbons that remain in and around the resin after the first stage.

A vent recovery system is typically utilized to recover hydrocarbonsfrom the mixed hydrocarbon/inert purge gas stream exiting the purgevessel. Existing methods of recovering hydrocarbons from thepolymerization unit vent stream include for example: a) compression andcondensation with water and/or mechanical refrigeration (for examplecooling to −10° C.); and b) separation via pressure swing absorption(PSA) or membranes. In existing gas phase polyethylene plants, Option(a) is most commonly applied, but a combination of (a) and (b) has alsobeen used.

In a compression and condensation system, such as described in U.S. Pat.No. 5,391,656, a polymer purge bin vent stream, which contains inertgases, such as nitrogen, and various monomers, is treated in a series ofsteps that include: cooling to condense a portion of the reactor gasstream; separating the condensed liquids from the remainingnon-condensable gases; compressing the non-condensable gases; coolingthe compressed stream to promote further condensing, further liquid/gasseparation, and further recycle of condensed monomers. The compressionand cooling vent recovery system provide recovery of a high percentageof the heavier contained hydrocarbons, for example butene, isopentane,hexene, hexane, and other heavy alkenes and alkanes, through thecondensation process.

Another recovery method contemplated in the art involves cryogenic ventrecovery, wherein condensation of monomer from vent streams containingnitrogen is accomplished by vaporization of liquid nitrogen.Commercially available cryogenic vent recovery systems used forcryogenic vent recovery typically rely on importing liquid nitrogen fromanother facility at site, importing liquid nitrogen from an off-sitefacility, or sending the vent to an off site facility to recover thecondensable hydrocarbons as a refuse stream.

Polymerization processes that utilize only compression/condensation withnon-cryogenic cooling of vent gas for hydrocarbon recovery can recovermost of the C4 and heavier hydrocarbons but will typically recover onlyabout 0 to 50% of the vented ethylene. Furthermore, the uncondensednitrogen contains significant amounts of heavy hydrocarbons, which maypreclude using it as a resin drying or purge gas. To reach a higherethylene recovery and achieve a higher recovered gas quality, furthervent recovery processing is required.

U.S. Pat. No. 6,576,043 describes a process for the separation of a gasmixture comprising nitrogen and at least one hydrocarbon from apolyethylene or polypropylene production plant in which nitrogen isutilized to purge solid particles of polymer product. The gas mixture isseparated in an adsorbent bed by a Pressure Swing Adsorption (PSA)process

U.S. Pat. No. 6,706,857 describes a process for the production of apolyolefin, wherein an olefin monomer is polymerized and a residualmonomer is recovered from a gas stream comprising the monomer andnitrogen. This process also uses a PSA process in which the monomer isadsorbed on a periodically regenerated silica gel or alumina adsorbentto recover a purified gas stream containing the olefin and a nitrogenrich stream.

U.S. Pat. No. 5,769,927 describes a process for treating a purge ventstream from a polymer manufacturing operation, the vent streamcontaining an olefin, such as ethylene or propylene, and a purge gas,such as nitrogen. The invention involves condensation, flashevaporation, and membrane separation. The process compresses and coolsthe purge vent stream; flashes a condensed portion to partially removeamounts of purge gas; treats the uncondensed portion in a membraneseparation unit; and recirculates the flash stream and a mixed streamfrom the membrane to the condensation step.

U.S. Pat. No. 5,741,350 discloses a method and apparatus for recovery ofhydrocarbons from polyalkene product purge gas that yields an alkenemonomer recycled to the polymerization process and a vapor-rich inertgas. The alkene monomer is condensed and separated at low temperaturefrom the inert gas, flashed and vaporized to provide refrigeration forthe condensation step, and recycled to the polymerization process.

Other background references in this respect include U.S. Pat. Nos.4,188,793, 4,727,723, 5,035,732, 5,421,167, 5,497,626, 5,626,034,5,979,177, 6,560,989, 6,576,805, 6,712,880, and 7,128,827, and U.S.Patent Application Publication Nos. 2005/0229634 and 2005/0159122.

Step (b)

In step (b), to substantially terminate these polymerization reactionswithin the reactor, polymerization inhibitors or “catalyst killers”,preferably comprising at least one irreversible catalyst killer, areemployed. For the purposes of this patent specification, the catalystkillers do not include that minor portion of catalyst killers that maybe contained in the monomer or comonomer feed streams during normalpolymerization conditions (for example, internal olefins).Cyclohexylamine can be used as irreversible catalyst killer.Cyclohexylamine can thus be introduced to at least partly deactivate thefirst catalyst. The term ‘at least partly deactivate’ is hereinunderstood to mean that the catalyst productivity is decreased by atleast 80%, preferably at least 90%. Preferably, the catalystproductivity is decreased by about 100%, i.e. the catalyst isdeactivated.

There are two general types of polymerization inhibitors. First,reversible catalyst killers which may be used in the invention are thosesuch as, but not limited to, for example, carbon monoxide (CO), carbondioxide (CO2), internal olefins, 2-butene and the like, internal dienes,2-4 hexadiene and the like, alkenes and butadienes. Reversible catalystkillers typically initially inhibit catalyst activity and polymerizationfor a period of time, but, do not irreversibly deactivate the catalyst.In fact, after a period of time under normal polymerization conditionsthe catalysts reactivate and polymerization will continue. Two or moreirreversible catalyst killers can also be used in combination. Thesereversible catalyst killers can be used in any combination or order ofintroduction in the process of this invention.

Second, there are irreversible catalyst killers, those killers thatirreversibly inactivate a catalyst's ability to polymerize olefins.According to the invention, cyclohexylamine is used as the irreversiblecatalyst killer.

In some embodiments of the invention, only cyclohexylamine is used asthe irreversible catalyst killer.

In some embodiments of the invention, one or more known furtherirreversible catalyst killer can be used, e.g. oxygen, water (H₂O),alcohols, glycols, phenols, ethers, carbonyl compounds such as ketones,aldehydes, carboxylic acids, esters, fatty acids, alkynes such asacetylene, nitriles, nitrous compounds, pyridine, pyroles,carbonylsulfide (COS) and mercaptans. Amines other than cyclohexylaminemay also be used as the additional irreversible catalyst killer. Theamine compounds used as irreversible catalyst killers in the presentinvention may preferably be an amine comprising a hydrocarbon group withat least eight carbon atoms, more preferably with at least twelve carbonatoms. An amine compound used as irreversible catalyst killer canthereby preferably be a primary amine. Two or more irreversible catalystkillers can thereby also be used in combination.

In an embodiment of the present invention an amine compound used asirreversible catalyst killer is selected from the group consisting ofoctadecylamine, ethylhexylamine, 2-ethylhexylamine, cyclohexylamine,bis(4-aminocyclohexyl)methane, hexamethylenediamine,1,3-benzenedimethanamine,1-amino-3-aminomethyl-3,5,5-trimethylcyclohexane and6-amino-1,3-dimethyluracil.

These irreversible catalyst killers can be used in any combination ororder of introduction in the process of this invention.

At least one irreversible catalyst killer, especially for examplecyclohexalamine, can also be used with one or more other irreversiblecatalyst killers and/or one or more reversible catalyst killers,especially for example in step (b) according to the present invention.

It is thus not beyond the scope of this invention that a mixture of oneor more of these reversible and irreversible catalyst killers can becombined before introduction into a reactor, however, one of ordinaryskill in the art will recognize that some of these killers could reactwith each other and are thus better introduced separately.

Preferably, once the first incompatible catalyst feed has beeninterrupted, a reversible catalyst killer is introduced into the reactorfor a period of time sufficient to substantially deactivate the catalystin the reactor and thus, substantially preventing further polymerizationfrom occurring. This can be done for example in step (a) or in step (b).The use of the reversible catalyst killer decreases the likelihood ofsheeting and/or fouling occurring in the reactor where the process ofthe invention takes place within the reactor in which polymerization wasoccurring with the first catalyst. In embodiment of the invention, priorto introducing an irreversible catalyst killer, the first catalyst canbe rendered substantially inactive, or in other words, substantiallyincapable of polymerization by the introduction/use of a reversiblecatalyst killer. The preferred reversible catalyst killers of theinvention are CO and/or CO₂. The amount of reversible catalyst killerused depends on the size of the reactor and the quantity and type ofcatalysts and cocatalysts in the reactor. Preferably, the reversiblecatalyst killer of the invention can be used for example in an amountbased on the total gram atoms of the catalyst transition metalcomponents. However, where any activator or cocatalyst is used with thefirst catalyst, and such activator or cocatalyst is capable of reactingwith the second catalyst, the reversible catalyst killer can be used forexample in an amount based on the total gram atoms of catalysttransition metal components and any activator.

In some embodiments the reversible killer is used in amount greater than1 molar equivalent, preferably greater than 2 molar equivalents based onthe total gram atoms transition metal of the catalyst in the reactor.

In some embodiments once the reversible catalyst killer has beenintroduced into the reactor, a period of time of about 5 minutes to 24hours, preferably 1 to 12 hours, more preferably 1 to 6 hours and mostpreferably 1 to 2 hours passes before introducing an irreversiblecatalyst killer. Letting this time pass is meant by putting the reactor“on hold”. The duration can depend on the nature and amount of catalystand volume of the reactor. In a gas phase reactor there is a seed bedthat is typically very large in size and quantity of polymer. Thus, asufficient period of time is needed to allow the reversible catalystkiller to disperse throughout the reactor, particularly throughout anypolymer product within the reactor.

Once the reversible catalyst killer has been introduced into thereactor, in a preferred embodiment, an irreversible catalyst killer isintroduced into the reactor. As described above, cyclohexylamine is usedas the irreversible catalyst killer.

In a preferred embodiment the amount of irreversible catalyst killerintroduced into the reactor is in the range of 0.1 to 1000 molar ratioof irreversible catalyst killer to the total metal of the catalyst andany activator in the reactor, preferably 0.1 to 100, more preferablyabout 1 to about 10, even more preferably about 1 to about 5 and mostpreferably greater than about 1 to less than about 2. However, where anyactivator or cocatalyst is used with the first catalyst, and suchactivator or cocatalyst is capable of reacting with the second catalyst,the irreversible catalyst killer can be used in an amount based on thetotal gram atoms of catalyst transition metal components and anyactivator. In another embodiment, the irreversible catalyst killer canbe used in an amount in the range of 100% to 125% of that necessary tofully inactivate all of the active first catalyst. This allows tosubstantially deactivate the first catalyst (so that it can alsopreferably not reactive itself) before introducing a secondincompatible. This also to avoid an excess amount of irreversible killerthat could remain in the reactor and partially or totally deactivate thesecond incompatible catalyst upon its injection into the reactor.

As mentioned above, the amount of the irreversible catalyst killer to beadded may be determined based on the measurement of the static of thereactor.

In yet another embodiment once the irreversible catalyst killer has beenintroduced into the reactor a period of time of about 5 minutes to about24 hours, preferably about 1 hour to about 12 hours, more preferablyabout 1 hour to 6 hours and most preferably about 1 hour to 2 hourspasses before continuing the transitioning process. Again, the durationof exposure is for the same reasons stated for the reversible catalystkiller.

Step (b2)

Typically, in the process of the invention it is important tosubstantially free the reactor of impurities, particularly theirreversible catalyst killer, which can render the second catalystinactive upon its introduction into a reactor. Thus, an organometalliccompound may be introduced into the reactor in step (b2) which iscapable of reacting with cyclohexylamine.

The organometallic compound reacts with the irreversible catalystkiller, such as cyclohexylamine. Such organometallic compounds caninclude for example, BX₃ where X is a halogen, R¹R²Mg, ethyl magnesium,R⁴CORMg, RCNR, ZnR₂, CdR₂, LiR, SnR4 where R are hydrocarbon groups thatcould be the same or different.

The organometallic compounds useful are those compounds of Group 1, 2, 3and 4 organometallic alkyls, alkoxides, and halides. The preferredorganometallic compounds are lithium alkyls, magnesium or zinc alkyls,magnesium alkyl halides, aluminum alkyls, silicon alkyl, siliconalkoxides and silicon alkyl halides. The more preferred organometalliccompounds are aluminum alkyls and magnesium alkyls.

The most preferred organometallic compounds are the aluminum compound offormula (1) as described above. The organometallic compounds used instep c) may be same or different from the aluminum compound of formula(1) used for the preparation of the surface modifier as described above.

The organometallic compound reacts with the remaining catalyst killersuch as cyclohexylamine, which reactant is circulated in the reactor fora period of time before the second catalyst is introduced. The reactantacts as a continuity aid agent, which assists in reducing fouling and/orsheeting on the walls of the reactor and/or reactor components.

Step (b3)

During the polymerization with the first incompatible catalyst, gasesaccumulate within the reactor, which originate from the electron donorwhen the first catalyst is especially a Ziegler-Natta catalyst. Thesegases are typically poisonous to the first catalyst, particularly to thesecond incompatible catalyst. These gases for a traditionalZiegler-Natta catalyst include, for example, tetrahydrofuran (THF),ethanol, ethyl benzoate and the like. Also, the introduction of thereversible and irreversible catalyst killers also produce by-productsthat can be detrimental to any polymerization process.

Thus, before introducing the second incompatible catalyst the reactorcontents are subjected to what is known in the art as pressure purging.Typically the procedure is used in handling any air/moisture sensitivematerials to remove, purge, or reduce in the process of the invention,for example, the catalyst killers and by-products thereof and reactantsto a lower level.

Once this procedure is complete the gas composition in the reactorsystem is adjusted for the second catalyst. Hence, a gas composition forthe second polymerization reaction is introduced in the reactor in step(b3). For a given catalyst to produce a given product of a certaindensity and melt index, which generally depends on how well a catalystincorporates comonomer, a certain gas composition must be present in thereactor.

Generally the gas contains at least one alpha-olefin having from 2 to 20carbon atoms, preferably 2-15 carbon atoms, for example, alpha-olefin ofethylene, propylene, butene-1, pentene-1, 4-methylpentene-1,hexene-1,octene-1, decene-1 and cyclic olefins such as styrene. Other monomerscan include polar vinyl, dienes, norborene, acetylene and aldehydemonomers. In the preferred embodiment, the gas composition containsethylene and at least one alpha-olefin having 3 to 15 carbon atoms.

Typically, the gas composition also contains an amount of hydrogen tocontrol the melt index of the polymer to be produced. In typicalcircumstances the gas also contains an amount of dew point increasingcomponent with the balance of the gas composition made up of anon-condensable inerts, for example, nitrogen.

Depending on the second catalyst to be introduced into the reactor thegas composition, such as the comonomer and hydrogen gas concentrations,can be increased or decreased. In the preferred embodiment the gascomposition is decreased, particularly when a metallocene catalyst isutilized as the second catalyst in the process of the invention.

Typically, the reactant gas composition is diluted as above, forexample, by either pressure purging or flow purging procedures wellknown in the art. During this step, as discussed above, impurities suchas electron donors from the catalyst are also removed.

Step (b4)

Preferably, after step (b3) and before step (c), a continuity aid agentis introduced. The continuity aid agent may be the same or different asthe modifier as described above and is the reaction product of analuminum compound of general formula (1)

and an amine compound of general formula (2)

whereinR1 is hydrogen or a branched or straight, substituted or unsubstitutedhydrocarbon group having 1-30 carbon atoms,R2 and R3 are the same or different and selected from branched orstraight, substituted or unsubstituted hydrocarbon groups having 1-30carbon atoms andR4 is hydrogen or a functional group with at least one active hydrogenR5 is hydrogen or a branched, straight or cyclic, substituted orunsubstituted hydrocarbon group having 1-30 carbon atoms,R6 is a branched, straight or cyclic, substituted or unsubstitutedhydrocarbon group having 1-30 carbon atoms.

The continuity aid agent is added to the reactor as a further processaid for reducing fouling and or sheeting. The amount is generally in theorder of 0.01-0.1 mmol per gram of catalyst composition.

Particularly preferred as the continuity aid agent is the reactionproduct of tri-isobutylaluminum and octadecylamine.

Step (c)

Subsequently, the second catalyst is introduced into the reactor underreactive conditions. The second polymerization reaction is started. Thefirst catalyst is introduced from a first catalyst feeding system andthe second catalyst is introduced from a second catalyst feeding systemseparate from the first catalyst feeding system. This prevents the riskof a trace amount of the first catalyst remaining in the catalystfeeding system leading to the formation of unacceptable amount of gel,without the time-consuming physical cleaning of the catalyst feedingsystem. The physical cleaning of the catalyst feeding system typicallytakes 6-8 hours.

Although the invention has been described in detail for purposes ofillustration, it is understood that such detail is solely for thatpurpose and variations can be made therein by those skilled in the artwithout departing from the spirit and scope of the invention as definedin the claims.

It is further noted that the invention relates to all possiblecombinations of features described herein, preferred in particular arethose combinations of features that are present in the claims.

It is further noted that the term ‘comprising’ does not exclude thepresence of other elements. However, it is also to be understood that adescription on a product comprising certain components also discloses aproduct consisting of these components. Similarly, it is also to beunderstood that a description on a process comprising certain steps alsodiscloses a process consisting of these steps.

The invention is now elucidated by way of the following examples,without however being limited thereto.

EXAMPLES

The gas phase reactor system as schematically shown in FIG. 1 was usedfor the transition process. The gaseous feed streams are mixed togetherin a mixing tee arrangement and enters the reactor from the bottom, andpasses through a perforated distribution plate. The unreacted gas streamis separated from the entrained polymer particles, and is thencompressed, cooled, and recycled back into the reactor. Productproperties are controlled by adjusting reaction conditions (temperature,pressure, flow rates, etc.).

The polymerizations were conducted in a continuous gas phase fluidizedbed reactor having an internal diameter of 45 cm and a reaction zoneheight of 140 cm. The fluidized bed was made up of polymer granules. Thereactor was filled with a bed of about 40 kg of dry polymer particlesthat was vigorously agitated by a high velocity gas stream. The bed ofpolymer particles in the reaction zone was kept in a fluidized state bya recycle stream that works as a fluidizing medium as well as a heatdissipating agent for absorbing the exothermal heat generated withinreaction zone.

The individual flow rates of ethylene, hydrogen and comonomer werecontrolled to maintain fixed composition targets. The ethyleneconcentration was controlled to maintain a constant ethylene partialpressure. The hydrogen/ethylene flow ratio was well controlled tomaintain a relatively steady melt index of the final resin. Theconcentrations of all the gases were measured by an on-line gaschromatograph to ensure relatively constant composition in the recyclegas stream.

The solid catalyst was injected directly into the fluidized bed usingpurified nitrogen as a carrier. Its rate was adjusted to maintain aconstant production rate of about 12 kg/hr.

The reacting bed of growing polymer particles was maintained in afluidized state by the continuous flow of the make-up feed and recyclegas through the reaction zone. A superficial gas velocity of 0.40 m/secwas used to achieve this. The reactor was operated at a pressure andtemperature as shown in below tables. To maintain a constant reactortemperature, the temperature of the recycle gas is continuously adjustedup or down to accommodate any changes in the rate of heat generation dueto the polymerization.

The fluidized bed was maintained at a constant height by withdrawing aportion of the bed at a rate equal to the rate of formation ofparticulate product. The product was removed semi-continuously via aseries of valves into a fixed volume chamber. The so obtained productwas purged to remove entrained hydrocarbons and treated with a smallsteam of humidified nitrogen to deactivate any trace quantities ofresidual catalyst.

The properties of the polymer were determined by the following testmethods:

TABLE 1 Melt Index ASTM D-1238 - Condition E (190° C., 2.16 kg) DensityASTM D-1505 Bulk Density The resin is poured in a fixed volume cylinderof 400 cc. The bulk density is measured as the weight of resin dividedby 400 cc to give a value in g/cc. Average Particle Size The particlesize is measured by determining the weight of material collected on aseries of U.S. Standard sieves and determining the weight averageparticle size based on the sieve series used. Fines The fines aredefined as the percentage of the total distribution passing through a120 mesh standard sieve. This has a particle size equivalent of 120microns.

A transition was made from a polymerization using a Ziegler-Nattacatalyst to a metallocene catalyst.

The Ziegler-Natta catalyst was prepared by impregnating a titaniumchloride, magnesium chloride, and tetrahydrofuran (THF) complex intosilica support from a solution of THF. The silica is first dehydrated at600° C. to remove water and chemically treated with tri-ethyl aluminumto further remove the remaining water. The catalyst was treated byadding tri-n-hexylaluminum (TNHAL) and di-ethylaluminum chloride (DEAC)in isopentane solution and dried to become the final Ziegler-Nattacatalyst. The final catalyst had a titanium content of 1% and DEAC/THFmole ratio of 0.42 and TNHAL/THF ratio of 0.28.

The metallocene catalyst was made as follows:

At room temperature, 0.595 kg of diphenyl(2-indenyl)2ZrCl₂ was added to36.968 kg of a 30% methylaluminoxane solution (Al content 13.58 wt %)and stirred for 30 minutes to form activated metallocene. About 172 kgof dry toluene was added to 43 kg of silica 955 to form a silica slurry.At about 30° C., the activated metallocene was added to the silicaslurry under agitation. After the activated metallocene was added, thetemperature was increased to 50° C. After 2 hours at 50° C., Atmer 163(commercially available ethoxylated tertiary amine) was added. Afteraddition the mixture was kept at 50° C. for 1 hour. The reactiontemperature was then reduced to 30° C. The toluene was removed byfiltration and the obtained catalysts composition was dried by raisingthe temperature to 55° C. and using a flow of warm nitrogen. The Al/Zrratio used in this experiment was approximately 150.

Reference Experiment 1

The plant reactor was charged with 45 kilograms of a “seed bed” of alinear low density polyethylene having a flow index of 1.0 and densityof 918 kg/m³ produced earlier in another reactor through copolymerizingethylene and butene-1 using the Ziegler-Natta catalyst.

The transition was started by feeding TIBAL-Amine about an hour earlierthan the metallocene catalyst feeding at 0.12 kg/h feed rate at reactortemperature of 85° C., ethylene partial pressure of 8.5 bar, and C6/C2of 0.115.

The development of density and melt index (MI) over time at an averageT=87° C., and C6/C2=0.115 showed a typical stability of the resinproperties in terms of density and melt index as continuously producedfrom the pilot plant reactor and analyzed every two hours. The densitywas about 918 kg/m3 and the melt index was about 1.0.

The above catalyst under the above process condition produced thedesired product with a gel content (total defect area) of less than 40ppm according to the following method:

Method 1

A film was made by an extruder and the film was inspected with adetector from Optical Control Systems GmbH (OCS). The OCS equipmentmeasures the defects.

The equipment used consisted of an Optical Control Systems GmbH (OCS)Model ME-20 extruder, and OCS Model CR-8 cast film system, and an OCSModel FSA-100 gel counter. The ME-20 extruder consists of a ¾″ standardscrew with 3/1 compression ratio, and 25/1 L/D. It includes a feed zone,a compression zone, and a metering zone. The extruder utilizes all solidstate controls, a variable frequency AC drive for the screw, 5 heatingzones including 3 for the barrel, 1 for the melt temperature andpressure measurement zone, and one for the die. The die was a 150 mmfixed lip die of a “fishtail” design, with a die gap of about 5 mm.

The total defect area (TDA) of the film is defined as:TDA (ppm)=Total Defect Area (mm²)/Inspected Area (m²)

The gel size (μm) is classified in

-   -   0-300    -   300-600    -   600-1000    -   1000-1200    -   >1200

The reactor was opened and the reactor wall was inspected. The reactorwall was clean with no wall fouling.

It can therefore be concluded that a satisfactory copolymer can beobtained by copolymerizing using the metallocene catalyst.

Reference Experiment 2

The catalyst feeder was charged with the Ziegler-Natta catalyst forpriming the catalyst feeder with the Ziegler-Natta, followed by dumpingand intensive purging with nitrogen.

Nitrogen purging was done continuously for about three hours. Oncepurging was done, priming with a metallocene catalyst was done throughcharging 150 g of the catalyst to the catalyst feeder followed byintensive mixing inside the catalyst reservoir or tank; a non-rotatingcomponent adjacent to the metering disc.

After an hour of mixing, the metallocene catalyst used for priming wasdumped to flush the whole feeder system that comprises a metering disc;a surface of contact between the metering disc and the non-rotatingcomponent, a drive shaft, a pickup section; and an injection tube.

Once this was done, intensive purging of the catalyst feeder viapurified nitrogen was done aiming at removing any remaining“contaminated” metallocene catalyst. The above procedure of catalystfeeder's priming and purging was repeated three times using themetallocene catalyst. Subsequently, 300 g of the metallocene catalystwas introduced to the catalyst feeder.

Subsequently, the same procedure of charging the reactor with resin andfeeding of TIBAL-Amine was followed as the reference experiment 1:

The reactor picked up immediately and within four hours ofpolymerization, the production rate reached about 9.5 kg/h. No suddenincrease in production rate was observed nor any change in the measureddensity and melt index.

Since there was no free THF in the reactor from a previouspolymerization using Ziegler-Natta catalyst, there was no effect on theprogression of resin properties of melt index and density.

The gel content (TDA) of the on-spec powder in terms of density and meltindex were analyzed and found to be extremely excessive exceeding anaverage of 20,000 PPM.

Such excessive gels were not expected due to the intensive purging andpriming done to the catalyst feeder.

Reference Experiment 3

After reference experiment 2, priming and flushing with the metallocenecatalyst was done in the same way as in reference experiment 2.Subsequently the catalyst feeder was charged with 320 g of themetallocene catalyst.

Expectedly, the reactor picked up immediately and within two hours ofpolymerization, the production rate reached about 10 kg/h without anychange in the measured density and melt index.

Since there was no free THF in the reactor from a previouspolymerization using Ziegler-Natta catalyst, there was no effect on theprogression of resin properties of melt index and density.

The gel content (TDA) of the on-spec powder in terms of density and meltindex were analyzed and found to be extremely excessive exceeding anaverage of 10,500 PPM.

Such excessive gels were not expected due to the intensive purging andpriming done to the catalyst feeder.

Most of the observed gel was very high molecular weight gel.

Reference Experiment 4

Reference experiment 2 was repeated except that the catalyst feederprimed with M1 catalyst was physically cleaned before being fed with ametallocene catalyst. The gel content (TDA) of the obtained copolymerwas only up to 25 PPM.

Preparation of M1 Catalyst:

Under a dry nitrogen atmosphere, a Schlenk flask was charged with silica(Davison 955, 33 g), previously calcined at 600° C. for 4 hours, and 19ml of 1 M of triethylaluminum (TEAL) in isopentane was added to thesilica to form a slurry. The slurry was kept at 37° C. for 1.0 hour.Then, 4 g of MgCl2 and 2.46 g of TiCl3 were dissolved in 1.5 liter ofTHF (100%) at 75° C. for 2 hours in a three nick bottom flask (Mg/Timolar ratio of 3.1). After dissolving MgCl2-TiCl3 precursor in THF thesolution was transferred into a Schlenk flask with TEAL on Silica andmixed for another hour at 75° C. Drying took place at 105° C. then 100°C. under nitrogen purge to reach 14.0 weight % THF in the final driedcatalyst powder. Finally, 4.1 g of neat DEAC was added to the previouslydried powder and mixed for 20 minutes followed by the addition of 4.8 gof TnHAL for 30 minutes then drying took place at 65° C. to obtain thefree flowing catalyst.

From reference experiments 2-4, it can be concluded that the reason forthe high level gellation is the Ziegler-Natta catalyst remaining in thecatalyst feeder system. An amount of Ziegler-Natta catalyst remains inthe catalyst feeder even after intensive purging, which is sufficientfor interfering with the copolymerization process using the metallocenecatalyst.

It can be concluded that this problem can be solved by using separatecatalyst feeders for the Ziegler-Natta catalyst and for the metallocenecatalyst.

The invention claimed is:
 1. A process for transitioning from a firstcontinuous polymerization reaction in a gas phase reactor conducted inthe presence of a first catalyst to a second polymerization reactionconducted in the presence of a second catalyst in the gas phase reactorwherein the first and second catalysts are incompatible, the processcomprising: (a) discontinuing the introduction of the first catalystfrom a first catalyst feeding system into the gas phase reactor; (b)introducing a catalyst killer to at least partially deactivate the firstcatalyst in the gas phase reactor; and (c) introducing into the gasphase reactor the second catalyst from a second catalyst feeding systemseparate from the first catalyst feeding system.
 2. The processaccording to claim 1, wherein the first catalyst is a Ziegler-Nattacatalyst and the second catalyst is a metallocene catalyst.
 3. Theprocess according to claim 1, wherein the second catalyst is ametallocene catalyst composition comprising a support containing ametallocene catalyst, a catalyst activator and an optional modifier. 4.A process for transitioning from a first continuous polymerizationreaction in a gas phase reactor conducted in the presence of a firstcatalyst to a second polymerization reaction conducted in the presenceof a second catalyst in the gas phase reactor wherein the first andsecond catalysts are incompatible, the process comprising: (a)discontinuing the introduction of the first catalyst from a firstcatalyst feeding system into the gas phase reactor; (b) introducing acatalyst killer to at least partially deactivate the first catalyst inthe gas phase reactor; and (c) introducing into the gas phase reactorthe second catalyst from a second catalyst feeding system separate fromthe first catalyst feeding system, wherein the second catalyst is ametallocene catalyst composition comprising a support containing ametallocene catalyst, a catalyst activator and an optional modifier, andwherein the metallocene catalyst is selected from the group consistingof: [ortho-bis(4-phenyl-2-indenyl)-benzene]zirconiumdichloride,[ortho-bis(5-phenyl-2-indenyl)-benzene]zirconiumdichloride,[ortho-bis(2-indenyl)benzene]zirconiumdichloride,[ortho-bis(2-indenyl)benzene]hafniumdichloride,[ortho-bis(1-methyl-2-indenyl)-benzene]zirconiumdichloride,[2.2′-(1.2-phenyldiyl)-1.1′-dimethylsilyl-bis(indene)]zirconiumdichloride,[2,2′-(1,2-phenyldiyl)-1,1′-diphenylsilyl-bis(indene)]zirconiumdichloride,[2,2′-(1.2-phenyldiyl)-1.1′-(1.2-ethanediyl)-bis(indene)]zirconiumdichloride,[2.2′-bis(2-indenyl)biphenyl]zirconiumdichloride and[2,2′-bis(2-indenyl)biphenyl]hafniumdichloride.
 5. The process accordingto claim 4, wherein the catalyst killer comprises cyclohexylamine.
 6. Aprocess for transitioning from a first continuous polymerizationreaction in a gas phase reactor conducted in the presence of a firstcatalyst to a second polymerization reaction conducted in the presenceof a second catalyst in the gas phase reactor wherein the first andsecond catalysts are incompatible, the process comprising: (a)discontinuing the introduction of the first catalyst from a firstcatalyst feeding system into the gas phase reactor; (b) introducing acatalyst killer to at least partially deactivate the first catalyst inthe gas phase reactor; (b2) introducing an organometallic compound intothe reactor to react with the catalyst killer; (b3) introducing a gascomposition into the reactor for the second polymerization reaction;(b4) introducing a reaction product of an aluminum compound of generalformula (1)

and an amine compound of general formula (2)

 and (c) introducing into the gas phase reactor the second catalyst froma second catalyst feeding system separate from the first catalystfeeding system, wherein R₁ is hydrogen or a branched or straight,substituted or unsubstituted hydrocarbon group having 1-30 carbon atoms,R₂ and R₃ are the same or different and selected from branched orstraight, substituted or unsubstituted hydrocarbon groups having 1-30carbon atoms, R₄ is hydrogen or a functional group with at least oneactive hydrogen, R₅ is hydrogen or a branched, straight or cyclic,substituted or unsubstituted hydrocarbon group having 1-30 carbon atoms,and R₆ is a branched, straight or cyclic, substituted or unsubstitutedhydrocarbon group having 1-30 carbon atoms.
 7. The process according toclaim 6, wherein the compound (1) is tri-isobutylaluminum and thecompound (2) is cyclohexylamine, octadecylamine, 2-ethylhexylamine,ethylhexylamine, bis(4-aminocyclohexyl)methane, hexamethylenediamine,1,3-benzenedimethanamine,1-amino-3-aminomethyl-3,5,5-trimethylcyclohexane and6-amino-1,3-dimethyluracil or a mixture thereof.
 8. The processaccording to claim 6, wherein the polymerization is conducted in afluidized bed reactor.
 9. The process according to claim 6, wherein thefirst continuous polymerization reaction is operated in a condensed modein which 5-17.4 wt % of the gas composition entering the gas phasereactor is liquid or a supercondensed mode in which more than 17.4 wt %of the gas composition entering the gas phase reactor is liquid.
 10. Theprocess according to claim 6, wherein the gas phase reactor is amulti-zone reactor operable in condensed mode, which multi-zone reactorcomprises a first zone, a second zone, a third zone, a fourth zone and adistribution plate, wherein the first zone is separated from the secondzone by the distribution plate, wherein the multi-zone reactor isextended in the vertical direction, wherein the second zone of themulti-zone reactor is located above the first zone and wherein the thirdzone of the multi-zone reactor is located above the second zone, andwherein the fourth zone of the multi-zone reactor is located above thethird zone, wherein the second zone contains an inner wall, wherein atleast part of the inner wall of the second zone is either in the form ofa gradually increasing inner diameter or a continuously opening cone,wherein the diameter or the opening increases in the vertical directiontowards the top of the multi-zone reactor, wherein the third zonecontains an inner wall, wherein at least part of the inner wall of thethird zone is either in the form of a gradually increasing innerdiameter or a continuously opening cone, wherein the diameter or theopening increases in the vertical direction towards the top of themulti-zone reactor, and wherein the largest diameter of the inner wallof the third zone is larger than the largest diameter of the inner wallof the second zone.
 11. The process according to claim 6, wherein areversible catalyst killer is introduced to render the first catalystinactive.
 12. The process according to claim 4, wherein the optionalmodifier is present and is a reaction product of an aluminum compound ofgeneral formula (1)

and an amine compound of general formula (2)

wherein R₁ is hydrogen or a branched or straight, substituted orunsubstituted hydrocarbon group having 1-30 carbon atoms, R₂ and R₃ arethe same or different and are selected from branched or straight,substituted or unsubstituted hydrocarbon groups having 1-30 carbonatoms, R₄ is hydrogen or a functional group with at least one activehydrogen, R₅ is hydrogen or a branched, straight or cyclic, substitutedor unsubstituted hydrocarbon group having 1-30 carbon atoms, and R₆ is abranched, straight or cyclic, substituted or unsubstituted hydrocarbongroup having 1-30 carbon atoms, or [B] an amine compound of generalformula (3)

where R₇ is hydrogen or a linear or branched alkyl group of from 1 to 50carbon atoms, R₈ is a hydroxy group of a (CH₂)_(x) radical and x is aninteger from 1 to
 50. 13. The process according to claim 12, wherein areversible catalyst killer is introduced to render the first catalystinactive.
 14. The process according to claim 6, wherein the compound (1)is tri-isobutylaluminum and the compound (2) is cyclohexylamine; and themetallocene catalyst is selected from the group consisting of:[ortho-bis(4-phenyl-2-indenyl)-benzene]zirconiumdichloride,[ortho-bis(5-phenyl-2-indenyl)- benzene]zirconiumdichloride,[ortho-bis(2-indenyl)benzene]zirconiumdichloride,[ortho-bis(2-indenyl)benzene]hafniumdichloride,[ortho-bis(1-methyl-2-indenyl)-benzene]zirconiumdichloride,[2.2′-(1.2-phenyldiyl)-1.1′-dimethylsilyl-bis(indene)]zirconiumdichloride,[2,2′-(1,2-phenyldiyl)-1,1′-diphenylsilyl-bis(indene)]zirconiumdichloride,[2,2′-(1.2-phenyldiyl)-1.1′-(1.2-ethanediyl)-bis(indene)]zirconiumdichloride,[2.2′-bis(2-indenyl)biphenyl]zirconiumdichloride and[2,2′-bis(2-indenyl)biphenyl]hafniumdichloride.
 15. The processaccording to claim 13, wherein the catalyst killer comprisescyclohexylamine.
 16. The process according to claim 13, wherein thepolymerization is conducted in a fluidized bed reactor.
 17. The processaccording to claim 8, wherein the first continuous polymerizationreaction is operated in a condensed mode in which 5-17.4 wt % of the gascomposition entering the gas phase reactor is liquid or a supercondensedmode in which more than 17.4 wt % of the gas composition entering thegas phase reactor is liquid.
 18. The process according to claim 8,wherein the gas phase reactor is a multi-zone reactor operable incondensed mode, which multi-zone reactor comprises a first zone, asecond zone, a third zone, a fourth zone and a distribution plate,wherein the first zone is separated from the second zone by thedistribution plate, wherein the multi-zone reactor is extended in thevertical direction, wherein the second zone of the multi-zone reactor islocated above the first zone and wherein the third zone of themulti-zone reactor is located above the second zone, and wherein thefourth zone of the multi-zone reactor is located above the third zone,wherein the second zone contains an inner wall, wherein at least part ofthe inner wall of the second zone is either in the form of a graduallyincreasing inner diameter or a continuously opening cone, wherein thediameter or the opening increases in the vertical direction towards thetop of the multi-zone reactor wherein the third zone contains an innerwall, wherein at least part of the inner wall of the third zone iseither in the form of a gradually increasing inner diameter or acontinuously opening cone, wherein the diameter or the opening increasesin the vertical direction towards the top of the multi-zone reactorwherein the largest diameter of the inner wall of the third zone islarger than the largest diameter of the inner wall of the second zone.19. The process according to claim 11, wherein the reversible catalystkiller is CO.
 20. The process according to claim 6, wherein the compound(1) is tri-isobutylaluminum and the compound (2) is cyclohexylamine.